Tegra: Control inclusion of helper code used for asserts

One assert depends on code that is conditionally compiled based on the
DEBUG define. This patch modifies the conditional inclusion of such code
so that it is based on the ENABLE_ASSERTIONS build option.

Change-Id: Ic5659a3db8632593b9d2e83dac6d30afd87c131d
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>